#include<fstream>
using namespace std;
bool prim[2100100];
int n;
int ciur() {
    int i,j,cont=1;
    for(i=3;i<=n;i+=2)
        if(!prim[i]) {
            cont++;
            for (j = i*i; j <= n; j += i << 1)
                prim[j]=1;
        }
    return cont;
}
int main() {
    ifstream in("ciur.in");
    in>>n;
    in.close();
    ofstream out("ciur.out");
    out<<ciur()<<'\n';
    out.close();
    return 0;
}